Genomic imprinting results in the preferential expression of the paternally, or maternally inherited allele of certain genes. Imprinted genes are highly expressed in the adult and developing brain, and this mode of epigenetic regulation of gene expression is essential for normal brain development and function. Moreover, defects in imprinted genes have been implicated in various mental illnesses including autism, psychosis, and mental retardation. We have recently developed a genome-wide sequencing strategy that led to the discovery of over 1300 new imprinted loci in the adult and developing brain and we have demonstrated that the repertoires of imprinted genes in the developing brain and adult male and female cortex are different. This suggests that genomic imprinting is a major and dynamic mode of epigenetic regulation, which has direct implications for the understanding of brain development and function, and of mental illnesses. The present proposal aims to unravel parental bias of gene expression in a genetically defined cortical cell population, the pan/albumin (PV) positive inhibitory interneurons that are thought to play major roles in the maturation of cortical circuits, and to be affected in various mental disorders. We will first optimize experimental strategies to purify PV cell-specific transcripts, and assess the nature of genes displaying parent of origin expression bias in mature PV interneurons. We will then compare the repertoire of imprinted genes in adult and developing PV cells, as well as in males and females. Finally we will investigate how the imprinted status of these gene is affected in mouse models of mental illness such as autism, schizophrenia and anxiety disorders. Our study will rely on the expertise and reagents from the Hensch group who has pioneered the study of PV-positive cortical interneurons function in the normal and pathological brain. In turn, our results will provide targets for further genetic, functional and circuit-wiring analysis by the Hensch and Lichtman's groups. The molecular and functional characterization of parental expression bias in PV cells will serve as a model for the experimental analysis of epigenetic controls of gene regulation in generically identified cortical cell types in the normal and pathological brain.